Héterogénéité de la chlorophylle in vivo

Abstract

A former study of chlorophyll fluorescence in Chlorella had lead to the distinction of several fractions of the chlorophyll holochrome: A photoreceptive fraction Chl₀ and two fractions Chl₁⁶⁸⁵ and Chl₁⁷²⁰ the excition of which was sensitized by the first one. The Chl₁⁶⁸⁵ fraction has a potochemical function and is responsible for the variable yield emission. The constant yield emission maily comes from Chl₀ and to a lesser extent from Chl₁⁷²⁰.

By studies of fluorescence polarisation, this scheme of excitation transfers is confirmed; moreover, the Chl₁⁷²⁰ fraction has a certain amount of direct absorption and a high degree of orientation.

The variation of fluorescence yield during the induction period is seen as resulting from the distribution of the Chl₁⁶⁸⁵ fraction between at least two forms: the non-fluorescent O form and the fluorescent P form. Action spectra of the Chl₁⁶⁸⁵ show in the far red a difference between the photochemical production of the P form and the excitation of its fluorescence. This difference can be understood in the theory of two photochemical systems of photosynthesis as resulting from the antagonistic action of each system on the P form.

The general scheme of electron transport in photosynthesis and the concept of structural separation of the sensitizers of the two systems are discussed.